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Aging Management of CANDU NPP
Concrete Structures
Julia Tcherner
Senior Civil Engineer
Candu Energy
IAEA Consultancy Meeting, Assessment and Ageing of Concrete Structures
May 29June 1, 2012
Outline
•CANDU Plants–Multi-unit
–Single unit (CANDU 6)
•Codes and Standards–How ageing is addressed
•Ageing Management
•Condition / Life Assessments–Problem areas
•Repairs
•Monitoring1
Multi – Unit CANDU
2
•18 operating units at 3 sites in
Ontario, Canada
• Darlington
• Bruce
• Pickering
•Typically several Reactor Buildings
are connected by pressure relief
duct to the same vacuum building
• Oldest
Pickering A (1971)
• Most Recent
Darlington (1993)
• Original Design Life
30 or 40 years
CANDU 6
3
• 11 CANDU 6 Operating Reactors
• 2 in Canada, 9 around the world
• Argentina
• China
• Korea
• Romania
•Fully posttensioned bonded
system (mat, cylinder, dome)
•Nonmetallic liner system
Outline
•CANDU Plants–Multi-unit
–Single unit (CANDU 6)
•Codes and Standards–How ageing is addressed
•Ageing Management
•Condition / Life Assessments–Problem areas
•Repairs
•Monitoring6
Canadian Standard Association (CSA)
7
• not-for-profit membership-based association serving business, industry, government and consumers in Canada and the global marketplace.
The purpose –
• to develop standards that address real needs, such as enhancing public safety and health, advancing the quality of life, helping to preserve the environment, facilitating trade.
• to help people understand standards through education and information products and services.
Standards for Concrete Containment
Structures
• First developed in late 1970s
• Revised in early 1990s
• Another cycle of revisions started in mid 2000s
• defines requirements for concrete containment structures of
nuclear power plants including requirements for: materials,
design,
construction,
examination and testing during construction,
proof pressure and leakage rate testing ,
inservice examination and testing.
CSA N287 Series
8
Standard for Safety Related Structures
9
CSA N291 - 08
• First edition of the Standard published in 2008
• This Standard specifies requirements for safetyrelated structures constructed of structural steel, reinforced concrete, and reinforced masonry
• This Standard also covers requirements for irradiated fuel storage facilities
• This Standards includes requirements for: – analysis – design– inspection– examination
10
• Consistent up-to-date standards for design and construction
of the new nuclear power plants are required.
• With aging of the nuclear power plants the necessity for
proactive approach to address emerging challenges was
recognized
• A need to allow industry to take advantage of the new level
of knowledge and experience was identified.
Recent Updates of the Standards - reasons
CSA N287 Series
CSA N287.1-93 (R2009) – currently being revised, General requirements for concrete containment structures for CANDU nuclear power plants
CSA N287.2-08, Material requirements for concrete containment structures for CANDU nuclear power plants
CSA N287.3-93 (R2009) – currently being revised, Design requirements for concrete containment structures for CANDU nuclear power plants,
CSA N287.4-09, Construction, fabrication, and installation requirements for concrete containment structures for CANDU nuclear power plants
CSA N287.5-11, Examination and testing requirements for concrete containment structures for nuclear power plants
CSA N287.6-11, Pre-operational proof and leakage rate testing requirements for containment structures for nuclear power plants
CSA N287.7-08, In-service examination and testing requirements for concrete containment structures for CANDU nuclear power plants
11
CSA N287 Series – Recently Updated Standards
N287.7 - 08
• Specifies uniform rules for
assessment of the structural
and leaktight integrity of
concrete containment
structures through systematic
and periodic examination.
• The fourth edition of the
Standard was issued in 2008
superseding the previous
editions published in 1996,
1980, and 1975.
12
CSA N287 Series – Recently Updated Standards
N287.7 - 08
• Main updates in 2008 edition: – revisions to the reference standards
– enhancements to address the lessons learned in implementation of the
standard
– enhancements to take advantage of recent advances in inservice
examination techniques
– requirements for trending of the observations made during inservice
examinations and tests were added
– requirements for inservice examination program and acceptance criteria
were added
– requirements for prestressing system integrity evaluation were enhanced
– new nonmandatory annex was added to allow for alternative option for
monitoring of the prestressing system behaviour
– another new nonmandatory annex was added to recognize performance
based approach to determining interval between the leakage rate tests.
13
CSA N287 Series – Recently Updated Standards
N287.2 - 08
• Specifies requirements for the materials used in concrete
containment structures of containment systems designated
as class containment components, parts, and appurtenances
in CANDU nuclear power plants.
• The fifth edition of the Standard was issued in 2008
superseding the previous editions published in 1991, 1982,
1977, and 1976.
14
CSA N287 Series – Recently Updated Standards
N287.2 - 08
• Main updates in 2008 edition: – revisions to the reference standards
– the use of various types of cement and supplementary cementing
materials was allowed to take advantage of the technological
advancements
– requirements for repair materials were added
– requirements for grout and grouting of the posttensioning system were
enhanced
– requirements for qualifications of the joint sealant materials were added
– requirements for qualifications of nonmetallic liner materials were
enhanced
– an alternative for seismic qualification of postinstalled mechanical anchor
bolts was included
– two nonmandatory annexes were added
15
CSA N287 Series – Recently Updated Standards
N287.4 - 09
• Specifies requirements for construction,
fabrication, and installation for concrete
containment structures.
• The fourth edition of the Standard was issued in
2009 superseding previous edition published in
1992, 1983, and 1977.
16
CSA N287 Series – Recently Updated Standards
N287.4 - 09
• Main updates in 2009 edition: new requirements have been added to improve the quality of
construction to address lessons learned in recent CANDU containment construction as well as those summarized in the US NRC Information
Notice 200817 Construction Experience with Concrete Placement.
changes were made to incorporate industry advances and good
practices and improve interfaces with revised CSA standards
· ensuring the uniformity and traceability of concrete,
· improving quality of mechanical splices installation, · improving corrosion protection of the prestressing tendons.
requirements for tolerances and deviations in installation of the
metallic parts were refined requirements for installation of joint sealant material were included
requirements for water stops and metallic liners were added.
17
CSA N287 Series – Recently Updated Standards
N287.5 - 11
• Specifies examination and testing requirements
that will ensure that concrete containment
structures are built using techniques and work
practices that meet the quality and standards
commensurate with the safety principles
necessary to comply with the Canadian nuclear
safety philosophy.
• The third revision of the standard was issued in
2011 superseding previous editions published in
1993 and 1981.
18
CSA N287 Series – Recently Updated Standards
N287.5 - 11
• Main updates in 2011 edition: – revisions to the reference CSA standards to enhance
the clarity and consistency of the standard scope and
its linkage to other CSA standards
– lessons learned in implementation of the standard
were incorporated
– recent advances in examination and testing
techniques were captured
19
CSA N287 Series – Recently Updated Standards
N287.6 - 11
• Specifies requirements for preoperational proof
and leakage rate testing of concrete containment
structures
• The fourth edition of the Standard was issued in
2011 superseding previous editions, published in
1994, 1980, and 1978 under the title Pre
Operational Proof and Leakage Rate Testing
Requirements for Concrete Containment
Structures for CANDU Nuclear Power Plants
20
CSA N287 Series – Recently Updated Standards
N287.6 - 11
• Main updates in 2011 edition: – revisions to the reference CSA standards to enhance the clarity and
consistency of the standard scope and its linkage to other CSA
standards
– lessons learned in implementation of the standard as well as recent
advances in examination and testing techniques were captured
– requirements for prestressing system integrity evaluation were
enhanced
– new nonmandatory annex was added to address requirements
for instrumented monitoring of the posttensioning system
21
Outline
•CANDU Plants–Multi-unit
–Single unit (CANDU 6)
•Codes and Standards–How ageing is addressed
•Ageing Management
•Condition / Life Assessments–Problem areas
•Repairs
•Monitoring 22
Canadian Nuclear Safety Commission (CNSC)
•CNSC regulates the nuclear
sector in Canada
•CNSC Regulatory Document
RD 334 – Aging Management
of Nuclear Power Plants
24
AMP Components
• Condition Assessment
• Identification of defects
• Prioritization
• Examination methods
• Evaluation criteria and frequency of periodic examinations
• Personnel qualifications
• Monitoring instrumentation
• Monitoring of environmental and operating conditions
• Monitoring performance of structure
• Repair
• Documentation requirements and data management
25
Condition Assessment
Current Condition
Health Prognosis
Assessment of construction
operation and maintenance
data against design basis
Assessment of
ARDMs and
their impact on
the ability of
structure to
meet its
functional
requirements
Assessment
of utility’s
programs to
manage
ARDMs
Obsolescence
26
Condition Assessment
To establish base
line condition
To identify
ARDMs
To identify critical
areas/components
To optimize AMP by using inspection and
monitoring techniques that are appropriate for
suspected degradation and concentrate efforts on
critical areas/components
Life Assessment / Condition Assessment
• RB Containment Structure
• RB Internal Structures
• Spent Fuel Bays
• Spent Fuel Dry Storage Facilities
• Spent Resin Tanks
• Liquid Waste Storage Tanks
• Underground Waste Storage Structures
• Turbine Block Foundation
• Cooling Water Buildings and Structures
28
Identification of Degradation
Concrete Chemical – leaching, sulphate attack,
acid attack, alkali aggregate reaction,
carbonation
Physical – freeze thaw cycles, salt
crystallization, abrasion/erosion,
temperature cycling, vibration (fatigue),
settlement, shrinkage
SteelChemical – corrosion
Physical - deformation
Physico-chemical – relaxation of
tendons
29
Identification of Degradation
Non-metallic Liners,
Sealants
Weathering, irradiation, wear,
delamination, exposure to elevated
temperatures,
Examination Methods –
Visual Inspection (including ROV)
33
Advantages
•simple
•effective
Limitations
•accessibility
Objective
•To identify any visible distress
Examination Methods –
Non-Destructive Examination
34
Advantages
•non destructive
Objectives
•To identify defect
•To detect degradation
•To quantify degradation
Limitations
•accessibility
•interferences
•local effects
Examination Methods –
Laboratory Testing
35
Advantages
•quantitative
Limitations
•destructive
•accessibility / radiation
•local effects
Objectives
•To verify degradation
•To determine possible cause
•To quantify extent
Evaluation Criteria and Frequency
36
Evaluation Criteria
ACI 349.3
• Acceptance without
further evaluation
• Acceptance after
review
• Condition requiring
further evaluation
Frequency
CSA N287.7 – concrete
containment
CSA 291 – safety related
structures
Personnel Qualification
• Members of the evaluation team
–performing CA,
–conducting periodic examinations,
–evaluating results
• Knowledge (education, training, experience)
–evaluation of structure material degradation / structural
integrity
–functional requirements of the nuclear civil structures
37
Monitoring Condition of the Structure and
Monitoring Stressors
38
Vibrating Wire Strain
Gauges
Fibre Optic Sensors
Thermocouples
Cast-in corrosion probes
Temperature
Humidity
Chemistry
Water level fluctuations
Problem Areas
1. Elastomeric material (i.e. joint sealant and
liner system)
2. Integrity evaluation of post-tensioning
system
3. Concrete is generally in good condition,
however:
• Parts exposed to moisture – leaching
• Ring beam and buttresses protective cover – freeze-thaw
• Areas around penetrations and fuel transfer structure – air leakage
during LRT
CSA N287.7 – In-service Examination and Testing
42
CSA N287.708
Prestressing systems used as principal reinforcement in concrete
containment structures shall be subject
to an integrity evaluation for conformance to the design
specifications to determine the effects of certain
timerelated factors, such as
(a) shrinkage and creep of the concrete;
(b) stress relaxation; and
(c) deterioration.
Integrity Evaluation of Post-tensioning System
Methods for Integrity Evaluation of
Post-tensioning System
43
• Instrumented Monitoring
• Test Beams
• Liftoff test and inspection
Test Beams
•Simple beams, 6 m long
•Constructed per the same specifications as Reactor
Building containment structure
•Stored under the same conditions as Reactor Building
(exposed to the environment)
•Tested at predetermined intervals–Tendons examination
–Flexural tests
–Liftoff tests
44
CSA N287.6 – Preoperational Proof and Leakage Rate Test
45
CSA N287.694
Instrumentation required in Clause
5.4.1 shall not be mandatory for non
prototype concrete components that
are similar in design to those which
have previously passed the pressure
test requirements.
CSA N287.611
Instrumentation shall be provided to
(a) evaluate the behaviour of the structure and
the actual stress values during preoperational
proof
testing; and
(b) be used for the life of the plant, as applicable,
to
(i) monitor deformation of the containment
structure at the time of leakage rate testing in
order to ensure the elastic behaviour of the
containment structure; and
(ii) verify the integrity of the prestressing system.
Integrity Evaluation of Post-tensioning System
Instrumented Monitoring
Purpose
•To detect response of the containment
structure to the pressure loading
–Data collected during proof pressure and
leak rate tests
•To detect any unusual trends and to
monitor timedependant changes in the
containment structure
–Data collected during operation
47
Outline
•CANDU Plants–Multi-unit
–Single unit (CANDU 6)
•Codes and Standards–How ageing is addressed
•Ageing Management
•Condition / Life Assessments–Problem areas
•Repairs
•Monitoring 51
Repair
• Consideration
–cause of distress
–behavior of the structure
• Casebycase approach
• List of qualified materials
–Containment (CSA N287.2)
52
CANDU Owners Group (COG)
•COG is a notforprofit corporation with voluntary
funding from CANDUowning utilities and AECL.
Currently COG Membership includes 5 Canadian and 6
offshore Members
•The activities of COG cover four Programs for
collaborative research, information exchange, joint
projects and regulatory affairs.
Concrete Working Group main areas of research
•Qualification of liners and sealants
•Integrity assessment of the posttensioning system
•Integrity of Spent Fuel Bay under elevated
temperature
•Nondestructive examination methods
Gentilly 1 - Prototype CANDU
• 250 MW CANDU plant
• Designed in late 1960s• Currently in a safe sustainable shutdown state Storage With Surveillance (SWS)
Concrete Repair Example – Ring Beam, Gentilly 1
• Visual inspection
• Concrete core analysis
• Overcore concrete stress
measurements
• In-situ stress measurement
• Inspection of cables
A study was undertaken to determine condition of
the reactor building
Investigation (cont’d)
Results
• Concrete deteriorated in the
areas of posttensioning
anchorages (AAR and freeze
thaw)
• The anchorage heads,
exposed tendons and rebars
were in a reasonably good
condition
• All measured stresses were
as expected –compressive,
generally in the design range
Repair Objectives
� Remove all unsound and unbonded
concrete
� Restore the concrete of the
ringbeam
� Protect pre-stressing anchorages
� Protect the repair and provide
durable solutions
� Improve aesthetics of the building
Pre-Qualification
• Material certificates and
acceptance• Production (work) procedures• Prequalifying workmanship test• Test repair prepared• Pullout test
Repair Methodology
� Area of the ring-beam, with a
significant amount of
degradation should be
properly repaired and sealed
in order to prevent future
water ingress into that
structural concrete
� Application of Glass Fiber
Reinforced Polymer (GFRP)
was recommended for the
ring-beam as a long-term
solution.
Motivation for Instrumentation Program
� First GFRP repaired CANDU structure
�Promote confidence in new experimental technologies
adopted in G1 repair
� Effectiveness and Performance of Material
�Repaired concrete
�GFRP
� Reliability and Effectiveness of Equipment
�Fiber optic sensor technology
�Remote monitoring system
Aging Management Program
• VWSG and FOS installed inside and outside of ring beam• Readings were taken during concrete pouring and hydration• Currently monitored semiannually as part of AMP.
Vibrating Wire Strain Gauge (VWSG)
• A VWSG enables measurements of local strain of concrete in the vicinity of the gauge.
• The strain variation is calculated by measuring the change in resonant frequency of the wire, which varies with changes in its tension, against a datum value.
-800
-600
-400
-200
0
200
400
600
Date
E-300/575
E-90/575
E-90/300
W -90/560
W -330/560
N-125/250
N-50/100
N-120/250
N-50/100
S-315/500
S-90/500
S -215/600
S-90/600
S -120/275
-15
-10
-5
0
5
10
15
20
25
30
35
Date
E-300/575
E -90/575
E -90/300
W -90/560
W -330/560
N-125/250
N-50/100
N-120/250
N-50/100
S-315/500
S-90/500
S-215/600
S-90/600
S-120/275
VWSG
Results
Total
concrete
strain
Temperature
VWSG Results (cont’d)
-600
-400
-200
0
200
400
600
Date
E-300/575
E-90/575
E-90/300
W-90/560
W-330/560
N-125/250
N-50/100
N-120/250
N-50/100
S-315/500
S-90/500
S-215/600
S-90/600
S-120/275
Concrete Strain after Temperature Compensation
Fabry-Perot (FP) Sensor• measuring a gap shift or cavity length between two
facing fibre ends contained in a glass capillary
• reflected gap is shown on a readout screen
• FP sensors are able to provide compensated thermal
strain measurements
G1 ring beam repair and monitoring results
• The structural strain in the ring beam concrete measured by
most gauges is small and indicates no cracking.
• Both VWSG and FOS technologies are practical and effective
in monitoring
• GFRP has been effective in protecting the concrete from
further AAR damage
Conclusions and Lessons Learned
74
1. Degree of Degradation depends on:
• Quality of the structure as constructed!
• Aggressiveness of environment
2. Knowledge of degradation, experienced personnel is vital
3. Condition Assessment is instrumental
4. Prioritization is useful to optimize AMP
5. Simple NDEs that cover large areas are most useful
6. Three-tier acceptance criteria needs to be customized
7. Embedded and retrofitted proven instrumentation should
be used
8. Monitoring of the stressors (environmental and operating
conditions) and performance of the structure is paramount